In-Poor IGZO: Superior Resilience to Hydrogen in Forming Gas Anneal and PBTI

Abstract

Integrating In–Ga–Zn oxide (IGZO) channel transistors into silicon-based ecosystems requires the resilience of the channel material to hydrogen. Standard In-rich IGZO (In = 40 metal at. %) suffers from degradation under forming gas anneal (FGA) and hydrogen-driven positive bias temperature instability (PBTI). In this paper, we demonstrate scaled, top-gated transistors with an atomic layer deposition (ALD)-deposited In-poor (In ≤ 17 metal atom %) IGZO channel that shows superior resilience to hydrogen compared to those with an In-rich IGZO channel. These devices, fabricated with a 300 mm semiconductor fabrication plant (FAB) process, with dimensions down to WCH × LTG = 80 × 40 nm2, show excellent stability during a 2 h, 420 °C forming gas anneal (0.06 ≤ |ΔVTH| ≤ 0.33 V) and improved resilience to H in PBTI at 125 °C (down to no detectable H-induced VTH shift) compared to In-rich devices. We demonstrate that the mechanism of device degradation by H in the FGA is different from that of the H-induced VTH instability in PBTI. We argue that the first is due to oxygen scavenging by H, and the second, H release from the gate dielectric into the channel. We also show that resilience to H in one process does not automatically translate to resilience to H in the other. This significant improvement in IGZO resilience to H enables the use of FGA treatments during fabrication, needed for silicon technology compatibility, as well as further scaling and 3D integration, bringing IGZO-based technologies closer to mass production.